The researchers are studying plants grown in chambers that mimic conditions (including temperature, precipitation and carbon dioxide levels) similar to those projected by the Intergovernmental Panel on Climate Change in coming decades.

Bielory’s findings suggest that while pollen counts (the average number of pollen particles in a cubic yard of air over the course of a day) in the northeastern U.S. averaged at about 8,455 in 2000, they will surpass 11,412 by 2020 and will top 18,285 by 2040—possibly pushing as high as 21,735. In the past 25 years, for example, ragweed pollen has increased from Texas all the way up to Canada.

Not only are the average pollen counts likely to increase dramatically, but the allergy season is also set to start—and reach peak levels—much earlier in the year. In 2000, for example, pollen production began around April 15, but in 2020 it is expected to begin around March 27. Peak pollen production (increasing from 1,684 in 2000 to at least 1,844 in 2020) is likely to move from May 2 in 2000 to April 9 in 2020. And the warm season is not simply shifting its dates, but in most of North America, it is expanding by starting earlier and ending later, bringing more pollen for its duration.

Allergies are affecting an increasing segment of the population. Although there is currently no cure for seasonal allergies—and many people cope simply by using over-the-counter treatments to reduce symptoms—allergy shots can improve the body’s tolerance for the allergen. Allergies occur when the body’s immune system overreacts to a substance, such as tree pollen, grass, mold, dust mites, animal dander or a food. So shots work by slowly exposing the body to small amounts of the culprit substance. The drawback is that shots generally need to be given over time, and the tolerance generally does not last indefinitely. Bielroy recommends that, “allergy sufferers begin long-term treatment, such as immunotherapy, now” to decrease their reaction to increasing pollen levels to come.